fix: the native path never reported tier-gated posts (milestone 387 step A1)

`make_run_stats` has always declared `tier_gated_count`, and
DownloadDetailModal has always rendered it. gallery-dl populated it;
`ingest_core._result` did not — it built run_stats with six keys and let
the seventh default to 0, while the very same walk counted gated posts
into `gated_skipped` and spent the number on a log line.

So on Patreon, SubscribeStar and pixiv — the three platforms we now own —
the Downloads modal read "Tier-gated: 0" for a walk that skipped N
paywalled posts. A creator we've lost access to was indistinguishable
from a creator who stopped posting. Migrating Patreon off gallery-dl is
what dropped the signal.

Pass the count through, and tick it in the live-progress payload too, so
a long backfill on an inaccessible creator explains itself while it runs
rather than only at finalization. ActiveDownloadsPanel renders it only
when non-zero, coloured 'info' to match the severity FailingSourcesCard
already assigns tier_limited — this is not a failure.

Tests assert the run_stats key the UI actually reads rather than the
ingester's internal counter, so the guard tracks the property and not a
name. Falsification is structural: `make_run_stats` defaults the key to
0, so both assertions fail against the pre-fix call.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LNXXULQDjVZmbuNa2G9mD9

frontend/src/components/subscriptions/ActiveDownloadsPanel.vue

@@ -32,6 +32,13 @@
             v-if="e.live.errors" class="fc-active__count fc-active__count--err"
             title="errors"
           >✕ {{ e.live.errors }}</span>
+          <!-- Tier-gated posts (#874): not an error — the walk is working, the
+               content just isn't ours. Shown only when non-zero so a healthy
+               run stays uncluttered. -->
+          <span
+            v-if="e.live.gated" class="fc-active__count fc-active__count--gated"
+            title="posts skipped — no access at your tier"
+          >🔒 {{ e.live.gated }}</span>
           <span class="fc-active__count fc-active__count--posts" title="posts scanned">
             {{ e.live.posts }} posts</span>
         </span>
@@ -141,6 +148,9 @@ function elapsed (startedIso) {
 }
 .fc-active__count { color: rgb(var(--v-theme-on-surface-variant)); }
 .fc-active__count--err { color: rgb(var(--v-theme-error)); }
+/* Matches FailingSourcesCard's severity map, which already colours
+   tier_limited as 'info' — no-access is information, not a failure. */
+.fc-active__count--gated { color: rgb(var(--v-theme-info)); }
 .fc-active__count--posts { opacity: 0.7; }
 @keyframes fc-active-pulse {
   0%, 100% { opacity: 1; transform: scale(1); }